TouchEvent错误

Question

我有这个“总是在顶部按钮”并且当我在我的2.3.7 Ancdroid版本设备上点击它时出现错误，但是当我在我的4.2.2 Android设备上点击它时没有给错误！这是触摸事件的代码：

public class HUD extends Service implements OnClickListener, OnTouchListener, OnLongClickListener {
Button mButton;
@Override
public IBinder
onBind(Intent intent) {
return null;
}

@Override
public void onCreate() {
    super.onCreate();
    //mView = new HUDView(this);


    mButton = new Button(this);
    mButton.setId(1);
    mButton.setText("Button");
    mButton.setClickable(true);
    mButton.setOnTouchListener(this);


    WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.TYPE_PHONE, WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                    |  WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE, PixelFormat.OPAQUE);
    params.gravity = Gravity.LEFT | Gravity.TOP;
    params.setTitle("Load Average");
    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
    wm.addView(mButton, params);


}

@Override
public void onDestroy() {
    super.onDestroy();
    if(mButton != null)
    {
        ((WindowManager) getSystemService(WINDOW_SERVICE)).removeView(mButton);
        mButton = null;
    }
}

@Override
public boolean onTouch(View v, MotionEvent event) {   //onTouchEvent (where is the error)
    if(event.getX()<mButton.getWidth() & event.getY()>0)
    {
    Intent dialogIntent = new Intent(getBaseContext(), screen.class);
    dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    getApplication().startActivity(dialogIntent);
    HUD.this.stopSelf();
    }
    return false;
}


@Override
public void onClick(DialogInterface dialog, int which) {
    // TODO Auto-generated method stub
    Toast.makeText(this,"Click", Toast.LENGTH_SHORT).show();
}

@Override
public boolean onLongClick(View v) {
    // TODO Auto-generated method stub
    System.exit(1);
    return false;
  }    

}

这是2.3.7 Android设备触摸事件的日志猫：

07-21 00:01:47.960: E/AndroidRuntime(23542): FATAL EXCEPTION: main
07-21 00:01:47.960: E/AndroidRuntime(23542): java.lang.NullPointerException
07-21 00:01:47.960: E/AndroidRuntime(23542):    at com.example.screenshot.HUD.onTouch(HUD.java:75)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.view.View.dispatchTouchEvent(View.java:3881)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.view.ViewRoot.deliverPointerEvent(ViewRoot.java:2208)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.view.ViewRoot.handleMessage(ViewRoot.java:1881)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.os.Looper.loop(Looper.java:130)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at android.app.ActivityThread.main(ActivityThread.java:3706)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at java.lang.reflect.Method.invokeNative(Native Method)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at java.lang.reflect.Method.invoke(Method.java:507)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-21 00:01:47.960: E/AndroidRuntime(23542):    at dalvik.system.NativeStart.main(Native Method)

有人能帮帮我吗？谢谢......